Automatic and semi-automatic automotive transmissions typically utilize one or more internal clutch assemblies to transfer input torque from the vehicle's engine into transmission output torque at varying output speeds. With reference to FIGS. 13 and 14, a common example of transmission clutch assembly prior art is illustrated. FIG. 13 shows clutch assembly 1 in a disengaged mode of operation. FIG. 14 shows an enlarged view of clutch assembly 1 in an engaged mode of operation. Clutch assembly 1 includes a clutch housing 10, clutch apply piston 20, clutch apply cushion plate 30, multiple clutch reaction plates 40, multiple clutch friction plates 50, backing plate 60, and backing plate retaining ring 70. It should be noted that in some examples of prior art, clutch apply cushion plate 30 is not used or required.
Rotation and axial translation of the clutch assembly components occur about and along central axis 80. Clutch apply cushion plate 30, clutch reaction plates 40, and backing plate 60 have external teeth on their outer perimeters that engage corresponding internal teeth in clutch housing 10. Clutch friction plates 50 have an inner and outer diameter with internal teeth on their inner diameters that engage corresponding external teeth on an outer surface of a driven member, e.g., an intermediate or output shaft or housing (not shown for clarity). As partially illustrated in FIG. 14, clutch friction plates 50 typically consist of an intermediate, internally-toothed disk 52 with one or more layers of friction material 51 bonded to the disk.
Clutch reaction plates 40 and clutch friction plates 50 are interleaved to create a clutch pack 100. When disengaged, as shown in FIG. 13, there is a clearance L1 between clutch pack 100 and backing plate 60. Therefore, in the disengaged mode there is no axial force applied to clutch pack 100. In this mode there is no significant amount of frictional force developed within clutch pack 100, and, as such, clutch reaction plates 40 are free, absent any other outside forces, to rotate relative to clutch friction plates 50. Hence, in the disengaged mode, no torque is transmitted from the driving member, in this case clutch housing 10, to the driven member.
When clutch assembly 1 is in the engaged mode, as depicted in FIG. 14, force is applied axially to clutch pack 100 via clutch apply piston 20. When clutch apply piston 20 is applied, forcing clutch reaction plates 40 and clutch friction plates 50 together, the clutch reaction plates engage the clutch friction plates such that rotational forces from the central shaft are transmitted to clutch housing 10 (or vice versa). As the force is applied, clutch apply cushion plate 30 and clutch pack 100 translate axially until resisted by backing plate 60. Axial translation of backing plate 60 is limited by backing plate retaining ring 70, which is installed in a fixed groove in clutch housing 10. As the clutch components meet resistance from backing plate 60, the plates become compressed against each other. This compression generates frictional force between clutch reaction plates 40, backing plate 60, and clutch friction plates 50. Once engaged in this fashion, clutch pack 100 acts as a frictional drive coupling between a driving member, in this case clutch housing 10, and the driven member.
In order to achieve optimum clutch performance, proper face-to-face contact between the clutch components needs to be maintained during clutch engagement. Maximum contact surface area and even load distribution on the clutch plate friction contact surfaces are critical in order to minimize clutch slippage and/or the amount of heat generated due to friction. As the optimum contact conditions become compromised, excessive clutch slippage and heat generation tend to increase, leading to rapid clutch plate wear and the resultant poor clutch performance and durability.